1. Field of the Invention
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2006-288935, filed on Oct. 24, 2006, the disclosure of which is incorporated herein in its entirety by reference.
The present invention relates to a ring transmission apparatus and a signal processing method used in a packet ring network such as an optical ring network or the like, which transmits various types of data by using packets. Particularly, the present invention relates to a ring transmission apparatus and a signal processing method that deal with both real-time data such as voice and other types of data.
2. Description of the Related Art
In recent years, there is an increasing demand to construct packet networks that transmit packets to a network, such as an Ethernet™ network, with high liability. On this demand, attention has been given to packet ring networks, which can maintain communications even when a failure occurs, without loss of packets. With such a technical background, an optical ring transmission apparatus is proposed that is mounted with a single packet ring device for connecting to a ring network (see, for example, International Publication No. WO2003/015351). If such an optical ring transmission apparatus adopts a redundant configuration using two packet ring devices, a packet network with higher reliability than conventional ones can be realized. A schematic example of such an apparatus adopting a redundant configuration can be considered as shown in FIG. 1.
FIG. 1 shows a schematic configuration of an optical ring transmission apparatus connected to a ring network. This optical ring transmission apparatus 101 includes a packet ring device 102 incorporating a time-division-multiplex (TDM) switch section 103 and a packet switch section 104, and a packet ring device 105 incorporating a TDM switch section 106 and a packet switch section 107. The TDM switch section 103 is configured to transmit and receive data to/from a first ring 108 of a ring network 110, and the TDM switch section 106 is configured to transmit and receive data to/from a second ring 109 of the ring network 110.
The TDM switch sections 103 and 106 are also connected to a TDM switch 111 and are further connected to the packet switch sections 104 and 107, respectively. The packet switch section (104, 107) is connected to a packet switch 112 to perform multiplexing of packets into a virtual container and demultiplexing of a virtual container into packets. The TDM switch section (103, 106) multiplexes virtual containers received from the packet switch section (104, 107) and the TDM switch 111 into a multiplex signal and demultiplexes a multiplex signal received from the optical ring network 110 into virtual containers forwarded to the packet switch section (104, 107) and virtual containers forwarded to the TDM switch 111. A client network (not shown) is connected to the optical ring network 110 through the optical ring transmission apparatus 101.
In the optical ring transmission apparatus 101 as described above, the TDM switch section 103 and the packet switch section 104 are implemented in parallel in the packet ring device 102 in order to accommodate TDM traffic and packet traffic efficiently. Similarly, the TDM switch section 106 and the packet switch section 107 are implemented in parallel in the packet ring device 105. Packet traffic input from the client network is forwarded to a selected one of the packet switch sections 104 and 107 by the packet switch 112, where packets are processed directly to produce a virtual container. On the other hand, TDM traffic of virtual containers received from the client network is forwarded as it is to a selected one of the TDM switch sections 103 and 106 by the TDM switch 111.
The TDM switch section 103 multiplexes TDM traffic received from the TDM switch 111 and packet-traffic virtual containers received from the packet switch section 104 to produce a multiplex signal, which is further multiplexed by a TDM interface (not shown) into a TDM frame corresponding to the transport band of the ring network 110, and then sent out to the first ring 108. As for the packet ring device 105, the same signal processing is performed.
As described above, the optical ring transmission apparatus 101 can efficiently multiplex TDM traffic and packet traffic and output them onto the ring network 106. Therefore, not only a packet routing function and a TDM framing function are realized, but the TDM switch section (103, 106) and a TDM interface circuit are also implemented.
According to the optical ring transmission apparatus having the redundant configuration as shown in FIG. 1, even if a failure occurs in one of the packet ring devices 103 and 106, communication can be maintained by using the other ring device suffering no failure. Accordingly, it is possible to construct a network that is more reliable than the apparatus disclosed in the above-mentioned document (International Publication No. WO2003/015351). In addition, by adopting such a configuration, it is possible that the traffic input from the client network can be handled by any one of the packet ring devices. Therefore, this optical ring transmission apparatus can be applied not only to connection to a single-ring network but also connection to a multi-ring network or stackable ring network.
However, the TDM switch section and the TDM interface are conventionally implemented in a fixed manner inside the first packet ring device 102 and the second packet ring device 105. Accordingly, the transport band and transmission distance of the packet ring device are determined depending on the TDM switch section and the TDM interface, resulting in a problem that the optical ring transmission apparatus 101 lacks extensibility and flexibility.
Moreover, according to the conventional ring transmission apparatus shown in the above-mentioned document (International Publication No. WO2003/015351), the TDM switch, which processes voice traffic, and the rouging module, which processes data packet traffic, are implemented on a switch card that is a single package. Therefore, according to such a conventional system, the routing module, which processes packets, is implemented on the same switch card that has another switching function. Accordingly, this configuration also lacks the extensibility of the routing module and cannot adapt to a future update.
Here, the transport band means the transmission capacity that an optical ring transmission apparatus can transmit to the optical ring network or the transmission capacity that the optical ring transmission apparatus can receive from the optical ring network. An interface used in transmission of an optical signal generally has a fixed transmission capacity, and transmission/reception cannot be performed with a transmission capacity different from the fixed one. For example, 2.4 Gbps (gigabits per second) or 10 Gbps is used for the interface. In the case of an optical-signal interface, the properties of a received signal are degraded in proportion to the propagation distance depending on the wavelength range and dispersion characteristic of a light source employed. Such signal degradation also causes other restrictions.
To overcome such problems, it is necessary to provide a set of packet ring devices for each one of various transport bands and distances. This makes it difficult to reduce the cost of the optical ring transmission apparatus 101. Moreover, for the TDM switch sections 103 and 106, it is necessary to use those capable of multiplexing traffic, which increases the costs of the first and second packet ring devices 102 and 105.